1. Field of the Invention
The present invention relates to improved systems and methods for performing non-destructive testing and analyses of railroad rails. More particularly, the present invention is directed to systems and methods for identifying flaws and defects in underlying railroad rails using ultrasonic detection means mounted within fluid-filled tires, wherein the fluid within the tires is maintained at a constant, desired temperature through the use of one or more heat exchangers.
2. Description of the Related Art
From time to time, and for various reasons, the rails of a railroad track may develop one or more detrimental flaws or defects. Such adverse conditions may include transverse defects, vertical shear or split-head defects, horizontal shear or split-head defects or the like that may originate from manufacturing and construction processes, environmental factors or wear-and-tear from normal use. These flaws or defects are typically observed in the head of a rail, but may also be found within the web and feet of the rail, around the peripheries of the bolt holes, or any other portion of the cross-section of the rail. Due to the nature of railway travel, in which locomotives weighing tens of thousands of pounds regularly carry hundreds of tons of freight over rails while traveling at varying speeds, cracks within the rails may expand or propagate throughout the rail heads over time. Such flaws or defects that are left unattended or unaddressed can lead to a variety of problems, the most serious of which may include catastrophic rail failures or train derailments, and may pose serious financial, health and safety risks to goods and personnel, as well as the railway industry as a whole.
Rail failures may be predicted and avoided through routine non-destructive inspection, which may enable railway operators to identify and cure hidden or infinitesimal flaws or defects within rails before they manifest into problems of much greater magnitudes. To detect such flaws or defects, vehicles or rail car-mounted apparatuses including ultrasonic inspection equipment have been built to travel along a railroad track, and to continuously perform ultrasonic testing of the underlying rails in situ by transmitting ultrasonic beams into the rails and analyzing any portions of the beams that may be reflected off flaws or defects.
One example of an ultrasonic railroad rail inspection system for in situ rail inspection including a wheel assembly having a fluid-filled tire for maintaining rolling contact with the head of an underlying rail is disclosed in U.S. Pat. No. 7,849,748 B2 to Havira. According to the teachings of Havira, the tire forms a contact patch with a head of an underlying rail and includes an ultrasonic transducer supported within the tire for projecting an ultrasonic beam along a beam axis through the fluid and the tire, and into the head of the underlying rail. The ultrasonic beam propagates through the underlying rail and is reflected by any defects or flaws that may be present therein, which may cause some or all of the beam signal to be returned to the transducer or received by another ultrasonic detector. The reflected portions of the signal are then analyzed by one or more computer processors to determine the type, magnitude or location of the flaw or defect from which the signal was reflected.
When an ultrasonic transducer is suspended within a fluid-filled tire, such as is disclosed in Havira, the tire and fluid provide the transmission medium between the ultrasonic transducer and the underlying rail. Due to the nature of sound travel, the strength and quality of the ultrasonic signals that are both delivered and received by the transducer depend upon the speed of sound in the fluid.
The speed of sound of longitudinal sound waves in a medium is generally dependent upon the medium's compressibility and density. In a liquid medium, the speed of sound is typically calculated according to the Newton-LaPlace formula shown in Equation (1), below:
                    c        =                              K            ρ                                              (        1        )            
where c is the speed of sound in the medium; K is the bulk modulus of the medium, i.e., a measure of the medium's resistance to uniform compression; and ρ is the density of the medium.
Both the density and the bulk modulus (or compressibility) of a liquid are typically dependent upon the temperature of the liquid. In liquid water, the density varies widely within the range between the freezing and boiling temperatures of 0° C. and 100° C. (32° F. and 212° F.), respectively. For example, the density of water has been observed to follow a roughly parabolic plot between 0° and 100° C. (32° F. and 212° F.), with a peak density of approximately 1.0000 gram per milliliter (g/ml) at approximately 4° C. (39.2° F.), and with minimum densities of 0.9999 grams per milliliter (g/ml) at approximately 0° C. (32° F.), and 0.9581 grams per milliliter (g/ml) at approximately 100° C. (212° F.). Likewise, the bulk modulus of water also varies as a function of the temperature of the water, rising from a value of 293×103 pounds per square inch (psi), or 2.02 gigapascals (GPa), at 0° C. (32° F.), to a peak of 334×103 pounds per square inch (psi), or 2.30 gigapascals (GPa), at approximately 54.4° C. (130° F.), before descending to a value of 300×103 pounds per square inch (psi), or 2.07 gigapascals (GPa), at 100° C. (212° F.).
Variations in the density and the bulk modulus of a liquid at various temperatures result in concomitant variations in the speed of sound throughout the liquid. For example, in Speed of Sound in Pure Water, 52 J. Acoust. Soc. of America 1442 (1972), Del Grosso and Mader developed a fifth-order polynomial equation for estimating the speed of sound within pure water as a function of temperature. Del Grosso and Mader identified a peak sound velocity in pure water of 1,555.147 meters per second (m/s) at 74.172° C. (165.51° F.), as well as speeds of 1,402.388 meters per second (m/s) at 0° C. (32° F.) and 1,543.109 meters per second (m/s) at 100° C. (212° F.). Therefore, according to Del Grosso and Mader, the speed of sound in liquid water may vary across the range of temperatures in the liquid phase by over ten percent.
Variations in the speed of sound in a liquid as a function of temperature are particular critical to the inspection and analysis of railroad rails using ultrasonic detection means mounted within fluid-filled tires. Because the liquid acts as the primary transmission medium between the transducer and the rail head, changes in the sound propagation and attenuation properties of the liquid may create widely varying ultrasonic inspection results, either within an individual analysis, such as when the temperature of the fluid within the tire heats up due to friction after many miles of travel, or between analyses, such as when tests are performed at different times of the year or at different ambient temperatures. Unless the variation in fluid temperature is accounted for, the results of ultrasonic inspections may not be standardized, and may prove unhelpful in identifying flaws or defects within the rail. In such instances, the diagnosis and correction of potentially catastrophic failures may be unnecessarily delayed or completely overlooked.
It is an object of the present invention to overcome one or more of the drawbacks and/or disadvantages of the prior art described above.